The TEWI analysis is for a system lifetime of 10 years. The data represents the CO2 emissions and electrical energy input over a 10 year period. The method adopted follows the British Refrigeration Association/Institute of Refrigeration TEWI guidelines.

End of life recovery

It is assumed that 95% of the refrigerant charge is recovered after the 10 year period and not released to the environment

Refrigerant charge per kW load

Default values are shown. For a distributed DX system, the charge is 75% of the equivalent centralised system. For the cascade systems the medium temperature charge in kg per kW load is the same as for DX centralised. Secondary MT charge levels are based on those of a factory-built chiller.

Refrigerant leakage rate

Default values are shown. Distributed DX has a one-third lower leakage rate than a centralised system because it uses less pipe work and typically comprises a small factory-built system using hermetic scroll compressors. With this type of low-charge system, refrigerant loss can quickly be detected and stopped. Leakage rates for MT secondary cases are based on those for a factory-built chiller.

Generation factor

The generation factor is the quantity of carbon dioxide (CO2) emitted per kWh of electricity generated. It depends on the proportion of electricity generated from by fossil fuel, the type of fossil fuel and the efficiency of the generation. For example, where energy comes from a renewable source such as wind or hydro, the factor will be small. A default factor of 0.4 kg CO2/kWh for Europe and this is taken from European Commission Directorate-General for Transport and Energy (EU DG-TREN) 2003: European Energy and Transport Trends to 2030 (PRIMES), Brussels. The value may be changed by the user

GWP values

The GWP values are taken from IPCC (Intergovernmental Panel on Climate Change) Fourth Assessment Report: Climate Change 2007. The carbon embodied in the materials used to manufacture the refrigeration plant, in the production of the major components and refrigerant and the energy used in manufacturing and distribution are ignored.

Note: The chosen HFO refrigerants are similar to R134a in terms of volumetric refrigeration capacity.* According to ISO 817